The present invention relates to an array antenna for use in, e.g., a radar and more particularly to an array antenna capable of effecting transmission/receipt digital beam formation (DBF) and control over transmission/receipt digital polarization.
It is a common practice with an array antenna to effect transmission beam scanning and polarization control by adequately setting the amounts of phase shift of phase shifters arranged in transmission/receipt modules. It is also possible with the conventional array antenna to form receipt beams based on the combinations of a plurality of different polarization weights and a basic weight, i.e., multibeams of various polarizations.
However, a problem with the conventional array antenna is that control over beam formation during transmission is limited and prevents multiple functions available with receipt DBF, e.g., a receipt multibeam, a shaped beam and polarization control from being made most of. Specifically, during transmission, the phases of the antenna elements are limited by the minimum amounts of phase shift available with digital phase shifters. This, coupled with the fact that an amplitude must be set relying only on the ON/OFF state of module-by-module transmission. It is therefore difficult to form a desired transmission beam.
Another problem is that the number of beams which can be formed at the same time during receipt is limited to the number of complex product sum calculators available. This is because each complex product sum calculator have a single receipt output port.
Technologies relating to the present invention are disclosed in, e.g., Japanese Patent Laid-Open Publication Nos. 7-321537, 9-153721 and 9-162628.